Methods of quality control in concrete block production

ABSTRACT

The invention relates to a method of controlling the quality of blocks that are produced front face-up in a mold, and verifying the accuracy of the production of such blocks, to ensure that the blocks are manufactured with consistent quality and minimal block-to-block variability. Measurement locations are formed on the front faces of predetermined blocks. By measuring the distances between the measurement locations and the rear faces and comparing with a target distance, any variation provides an indication that the blocks are not being properly formed. The process variables, such as the alignment of the compression head and/or the pressure plates to the mold, can then be adjusted accordingly.

FIELD OF THE INVENTION

The invention relates generally to the manufacture of concrete blocks.More specifically, the invention relates to the manufacture of concreteblocks suitable for use in landscaping applications, such as retainingwalls, and methods of quality control relating to the production of suchblocks.

BACKGROUND OF THE INVENTION

Modem, high speed, automated concrete block plants typically make use ofmolds that are configured to produce multiple blocks simultaneously.These molds contain multiple mold cavities, where each cavity istypically open at the top and at the bottom. The molds are mounted inmachines which cyclically station a pallet below the mold to close thebottom of the mold cavities, deliver dry cast concrete into the moldcavities through the open top of the mold cavities, densify and compactthe concrete by a combination of vibration and pressure, and strip themold by a relative vertical movement of the mold and the pallet.

There is a demand for a concrete block that, when laid up into a wall orother structure with other blocks, has an exposed face that has anatural appearance so that a resulting wall constructed from a pluralityof the blocks appears to have been constructed with naturally-occurring,rather than man-made, materials.

Known methods for producing block faces with a natural appearance is bythe splitting process described in U.S. Pat. No. 5,827,015, or by thesplitting process described in U.S. Pat. No. 6,321,740.

Another method for achieving a block face that has a more naturalappearance than is achievable by known splitting processes is disclosedin U.S. Patent Application Publication No. 2003/0126821. As disclosed inPublication No. 2003/0126821, a mold is provided that has a plurality ofblock cavities arranged in a row, with each cavity being configured toproduce a concrete block with the block oriented with its front facefacing upward in the cavity. Pressure plates, also known as a “strippershoes,” are connected to a compression head. The pressure plates, whichhave a predetermined three-dimensional pattern formed therein, arepressed into dry cast concrete within the mold cavities by thecompression head to densify the concrete and impart the patterns to thefront faces of the blocks being formed in the cavities.

When imparting three-dimensional patterns to the faces of the blocksusing pressure plates, as in Publication No. 2003/0126821, it isimportant that the compression head and the pressure plates connectedthereto apply sufficient compaction pressure on the concrete in order toadequately densify the concrete. Insufficient densification of theconcrete can result in a block that does not have the expected anddesired strength properties. In addition, it is important that thecompression head and pressure plates be level so they come down straightand contact the dry cast concrete in the mold cavities with evenpressure across all of the cavities. If the head and the pressure platesare not level, uneven pressures may be exerted on the concrete in thecavities, thereby resulting in insufficient or uneven densification ofthe concrete in one or more of the cavities. Uneven densification canresult in a block having strength properties that vary greatly acrossthe block.

Further, insufficient and uneven densification can result inblock-to-block variations in the dimensions of the blocks, particularlythe depth of the block between the front and rear face of each block.Variability in the depths of the blocks can cause a wall or otherstructure built with the blocks to appear to be poorly constructed andto be visually unattractive.

There is a need for controlling the quality of blocks that are producedfront face-up in a mold, to ensure that the blocks are manufactured withconsistent quality and minimal block-to-block variability.

SUMMARY OF THE INVENTION

The invention relates to a method for producing concrete blocks frontface-up in a mold and that have a three-dimensional pattern imparted tothem by pressure plates. The invention also relates to a method ofcontrolling the quality of blocks that are produced front face-up in amold, and verifying the accuracy of the production of such blocks, toensure that the blocks are manufactured with consistent quality andminimal block-to-block variability.

The blocks are formed front face-up in a mold having at least one row ofblock-forming cavities, and a three-dimensional pattern is imparted tothe front face of each block by patterned pressure plates connected to acompression head. Predetermined ones of the pressure plates, for examplethe pressure plates associated with each end cavity, are configured toproduce measurement locations on the front faces of the blocks. Bymeasuring the distances between the measurements locations and the rearfaces of the blocks, any variations between the measured distances andthe target distances indicates that the compression head and thepressure plates connected thereto did not adequately compress theconcrete in the mold cavity, or are not oriented properly and need to beadjusted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a concrete block mold.

FIG. 2 is a top view of the row of block-forming cavities from the moldof FIG. 1.

FIG. 3 is a top view of another embodiment of a concrete block mold withtwo rows of block-forming cavities.

FIG. 4 is a cross-sectional view of one of the block-forming cavitiesand a patterned pressure plate that imparts a three-dimensional patternto the front face of a concrete block.

FIG. 5 is a perspective view of a block formed in one of theblock-forming cavities.

FIG. 6 is a perspective view of block formed with measurement locationsin one of the predetermined block-forming cavities.

FIG. 7 is a perspective view of block with an alternative arrangement ofmeasurement locations.

FIG. 8 is a top view of the concrete blocks formed in the mold of FIG. 2with a preferred arrangement of measurement locations.

FIG. 9 is a top view of the concrete blocks formed in the mold of FIG. 3with a preferred arrangement of measurement locations.

FIG. 10 is a top view of the concrete blocks formed in the mold of FIG.2 with an alternative arrangement of measurement locations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides a method for producing concrete blocksfront face-up in a mold and that have a three-dimensional patternimparted to the front faces by pressure plates. The invention alsorelates to a method of controlling the quality of blocks that areproduced front face-up in a mold, and verifying the accuracy of theproduction of such blocks, to ensure that the blocks are manufacturedwith consistent quality and minimal block-to-block variability.

Measurement locations are formed on the front faces of the blocks.Preferably, the measurement locations are formed on the front faces ofthe blocks located at the ends or corners of the mold. Measurementlocations at the ends or corners of the mold will tend to have greatersensitivity to production variability. However, the measurementlocations may be formed on the front faces of any of the blocks in themold, and the measurement locations may be formed at any position on thefront faces of the blocks. Preferably, to facilitate the measurement ofthe blocks in a production process, each measurement location definesthe same distance between it and the rear face of the respective blockwhen the blocks are correctly formed. However, because the front face ofa block is not necessarily parallel to the back face of a block, andbecause the measurement locations may be formed at any position on thefront face of a block, the measurement locations may not necessarilydefine the same distance between it and the rear face of the respectiveblock. In either case, if the measured distance from each measurementlocation to the rear face of the block equals the target distance, oneknows that the block has been properly formed with the expecteddensification of the concrete. On the other hand, if the measureddistance does not equal the target distance, that provides an indicationthat the concrete may not have been adequately densified and that theblock may not have been properly formed.

Further, if the measured distance on a block formed at one position ofthe mold does not equal the target distance, but the measured distanceon a block formed at another position of the mold does equal the targetdistance, one knows that the blocks have not been properly andconsistently formed within each of the cavities in the mold.

If the comparison between the measured distances and the targetdistances indicate that blocks have not been properly formed, correctiveaction may be taken. Variables that may be corrected include thealignment of the stripper shoe, the amount of concrete inserted intoeach mold cavity, the amount of force exerted by the stripper shoe, thedensity of the concrete mixture, or the composition of the concretemixture. The corrective action may also include the replacement of worncomponents.

FIG. 1 illustrates a mold assembly 4 comprising a mold 6 and acompression head assembly 8. The mold 6 comprises a row of block-formingcavities 10 that are visible in FIG. 2. In the embodiment illustrated inFIGS. 1 and 2, there are five block-forming cavities 10. The mold 6comprises a generally rectangular structure formed by a pair of sidewalls 22, 22′ and a pair of end walls 24, 24′. Division plates 30subdivide the mold 6 into the block-forming cavities 10.

Another example of an arrangement of mold cavities in a mold 20 isillustrated in FIG. 3. The mold 20 includes two rows of block-formingcavities 10 disposed side-by-side and separated by a dividing wall 26.In the illustrated embodiment, each row of the mold 20 includes nineblock-forming cavities 10.

Returning to FIG. 1, the head assembly 8 includes a compression head 12in the form of a plate. The head 12 is actuated by an actuatingmechanism in a manner known in the art so that the head 12 is moveablevertically up and down to bring about compaction of dry cast concretethat is deposited into the cavities 10 and to assist in stripping thepre-cured blocks from the block-forming cavities 10.

Connected to and extending from the bottom of the head 12 are aplurality of stand-offs 14, one stand-off for each block-forming cavity10. The stand-offs 14 are spaced from each other, with the longitudinalaxis of each stand-off oriented perpendicular to the plane of the head12 and extending generally centrally through the respectiveblock-forming cavity 10.

A pressure plate 16, also called a stripper shoe, is connected to theend of each stand-off 14. The stripper shoe 16 is rectangular in shapeand is dimensioned so that it may enter the respective cavity 10 throughthe top of the cavity to contact the concrete to compact the concrete,and to travel through the cavity during discharge of the pre-curedblock. Each stripper shoe 16 also has a face that comprises athree-dimensional pattern 18. When the stripper shoe 16 is pressed intothe concrete in the mold cavity, the three-dimensional pattern isimparted to the concrete in the cavity. Further details on using astripper shoe to compact concrete and impart a three-dimensional patternto the front face of a block, and for creating a suitablethree-dimensional pattern on the stripper shoe, are disclosed in U.S.Patent Application Publication No. 2003/0126821 which is incorporatedherein by reference in its entirety.

Turning now to FIG. 4, each cavity 10 is configured to form a blockwhere the front face of the block faces upward toward the open top ofthe mold cavity, and the rear face of the block rests on a pallet 28that is positioned underneath the mold cavities to temporarily close theopen bottoms of the mold cavities. The top, bottom and side faces of theblocks are formed by the side walls, end walls and division plates ofthe mold. Further details on a suitable mold cavity for forming a blockface-up in the cavity are disclosed in U.S. Patent ApplicationPublication No. 2003/0126821.

After dry cast concrete is deposited into the mold cavity 10, thestripper shoe 16 is brought down through the open top of the cavity 10to contact the concrete to compact the concrete and densify it. Theamount of densification of the concrete is selected so that the finishedblocks will have the desired weight, density, and performancecharacteristics. During compaction, the three-dimensional pattern isimparted to the front face of the block.

The general process of forming the blocks is disclosed in U.S. PatentApplication Publication No. 2003/0126821. Generally, the process isinitiated by mixing the dry cast concrete that will form the blocks. Drycast, no slump concrete is well known in the art. Once the concrete ismixed, it is transported to a hopper, which holds the concrete near themold. When it is desired to form blocks, the pallet 28 is positionedbeneath the mold so as to close the bottoms of the cavities 10. Theappropriate amount of dry cast concrete from the hopper is then loaded,via one or more feed drawers, into the block-forming cavities 10 throughthe open tops of the cavities 10. The process and equipment fortransporting dry cast concrete and loading a block-forming cavity arewell known in the art.

The dry cast concrete in the cavities 10 must next be compacted todensify it. This is accomplished primarily through vibration of the drycast concrete, in combination with the application of pressure exertedon the mass of dry cast concrete from above. The vibration can beexerted by vibration of the pallet underlying the mold (tablevibration), or by vibration of the mold box (mold vibration), or by acombination of both actions. The pressure is exerted through thecompression head 12 that is connected to the patterned stripper shoes 16that contact the mass of dry cast concrete from above. The timing andsequencing of the vibration and compression is variable, and dependsupon the characteristics of the dry cast concrete used and the desiredresults. The selection and application of the appropriate sequencing,timing, and types of vibrational forces is within the ordinary skill inthe art. Generally, these forces contribute to fully filling each cavity10, so that there are not undesired voids in the finished blocks, andalso to densifying the dry cast concrete so that the finished blockswill have the desired weight, density, and performance characteristics.

After densification, the pre-cured blocks are discharged from thecavities. Preferably, discharge occurs by lowering the pallet 28relative to the mold 6, while further lowering the stripper shoes 16through the mold cavities to assist in stripping the pre-cured blocksfrom the cavities. The stripper shoes are then raised upwardly out ofthe mold cavities and the mold is ready to repeat this production cycle.

Once the pre-cured blocks have been completely removed from thecavities, they can be transported away from the mold assembly forsubsequent curing. The blocks may be cured through any means known tothose of skill in the art. Examples of curing processes that aresuitable for practicing the invention include air curing, autoclaving,and steam curing. Any of these processes for curing the blocks may beimplemented by those of skill in the art.

Once cured, the blocks can be packaged for storage and subsequentshipment to a jobsite, and can then be used with other cured blocks informing a structure, such as a retaining wall.

To aid in determining whether the expected densification of the concretehas occurred, certain ones of the three-dimensional patterns on thestripper shoes 16 are configured to create measurement locations on theresulting front faces of the respective blocks. The measurementlocations are designed to provide reference points that are at apredetermined target distance, for example about 6 inches, away from therear face of the respective block when adequate densification hasoccurred. The target distance for any particular measurement location isdetermined based on the desired geometry of the block. To determinewhether unexpected densification has occurred, the distance between themeasurement locations and the rear face is measured and compared againstthe target distance. If the measured distance differs from the targetdistance, that provides an indication that unexpected densification,either greater or less than expected, has occurred, thereby indicatingthat the resulting blocks may not have the desired weight, density,geometry, and performance characteristics. Comparison of the measureddistance to the target distance may also provide an indication that themold cavity was not filled with the appropriate amount of concrete.

The measurement locations can comprise any small flat area that can bereplicated on the front faces of the selected blocks. For example, themeasurement locations can comprise flat spots that are created on thefront faces of the selected blocks by corresponding flat spots providedon the three-dimensional pattern on the stripper shoes. The measurementlocations may comprise any shape, such as circular, square, oval, orrectangular, or may be irregular in shape. The measurement locationsneed only be large enough to enable measurement of the distance from themeasurement locations to the rear face by an operator of the mold. Themeasurement locations are preferably kept small to minimize the visualobtrusiveness of the measurement location on the block face. However,the measurement locations should not be too small, because measurementlocations that are too small may prevent accurate use of a measurementinstrument, may cause the operator to have a difficult time locating themeasurement locations, and small amounts of residual concrete stuck tothe stripper shoe may cause the measurement location to be unusable.Preferably, the measurement locations are generally rectangular and atleast about ½ inch long and ⅛ inch wide. Further, the position of themeasurements locations on the front face is chosen so as to beunobtrusive on the resulting block face and to facilitate measurement ofthe distance. For example, the measurement locations can be on the frontface adjacent either the top or bottom face of the blocks.

FIG. 5 illustrates a block 38 formed in a cavity 10 of the mold 6, 20without measurement locations. Block 38 comprises a pair of convergingside faces 40, 42; a front face 44, a rear face 46, a top face 48, and abottom face 50. Reference to “top” and “bottom” refers to theorientation of the surfaces during the intended use of the block. Theblock 38 also includes a flange 52 that extends below the bottom face 50of the block 38 adjacent the rear face 46 and is designed to abutagainst the rear face of a block in the course below the block 38 toprovide a pre-determined set-back from the course below and providecourse-to-course shear strength. The front face 44 is an exposed,visible surface in a wall constructed from a plurality of the blocks andhas the three-dimensional pattern imparted to it by the stripper shoe toenhance the appearance of the wall.

FIG. 6 illustrates a block 54 that is similar to the block 38 but isformed with measurement locations 56 a, 56 b. Features in the block 54that are identical to features in the block 38 will be designated withthe same reference numeral. One of the measurement locations 56 a islocated on the front face 44′ near the corner defined by the side face42 and the bottom face 50. The other measurement location 56 b islocated on the front face 44′ near the corner defined by the side face40 and the bottom face 50. Other positions for the measurement locationsare possible. For example, FIG. 7 illustrates a block 58 withmeasurement locations 56 a′, 56 b′ formed near the corners defined bythe side face 42 and the top face 48 and by the side face 40 and the topface 48. Alternative configurations of the measurement locations arepossible.

The measurement locations can be formed on every block in every moldcavity 10. However, it is preferred to minimize the total number ofmeasurement locations so as to reduce the potential visual impact of themeasurement locations on the appearance of a wall or other structureconstructed from the blocks. Because variability in the production ofblocks may result from the pressure plates and compression head beingimproperly oriented relative to the mold, the number of measurementlocations should be sufficient to detect mis-orientation. A total of atleast three measurement locations formed on the blocks formed withinmold 6, 20 will allow the plane formed by the contact of the pressureplate with the concrete in the mold cavities to be determined. Thesemeasurement locations may be formed on any block or combination ofblocks within mold 6, 20.

Preferably, with reference to FIG. 8, the measurement locations areformed only on the front faces of the blocks associated with endcavities 10A and 10B, and with reference to FIG. 9, the measurementlocations are most preferably formed only on the front faces of theblocks associated with the corner cavities 10C, 10D, 10E, and 10F. FIGS.8 and 9 show the blocks formed within molds 6, 20 prior to the blocksbeing removed from the molds 6, 20. For clarity, FIGS. 8 and 9 show onlythe measurement locations on the block face and not any other featuresformed on the block face. Even more preferably, with reference to FIG.8, one measurement location is formed on the block associated withcavity 10A near the corner defined by side wall 22 and end wall 24, onemeasurement location is formed on the block associated with cavity 10Anear the corner defined by side wall 22′ and end wall 24, onemeasurement location is formed on the block associated with cavity 10Bnear the corner defined by side wall 22 and end wall 24′, and onemeasurement location is formed on the block associated with cavity 10Bnear the corner defined by side wall 22′ and end wall 24′. Thisarrangement provides the further advantage of positioning themeasurement locations where they are readily accessible to the moldoperator. With reference to FIG. 9, even more preferably, onemeasurement location is formed on the block associated with cavity 10Cnear the corner defined by side wall 22 and end wall 24, one measurementlocation is formed on the block associated with cavity 10D near thecorner defined by side wall 22′ and end wall 24, one measurementlocation is formed on the block associated with cavity 10E near thecorner defined by side wall 22 and end wall 24′, and one measurementlocation is formed on the block associated with cavity 10F near thecorner defined by side wall 22′ and end wall 24′. This arrangement alsoprovides the advantage of positioning the measurement locations wherethey are readily accessible to the mold operator.

Alternatively, FIG. 10 shows one possible alternative arrangement ofmeasurement locations 56 relative to the arrangement of blocks in a moldcavity 6, where a single measurement location 56 is located on the blocklocated adjacent to the block formed in mold cavity 10A and onemeasurement location 56 is located on the block located adjacent to theblock formed in mold cavity 10B. An additional measurement location islocated on the block formed in the middle cavity of the mold. However,many other combinations of locations of the measurement locations 56 arepossible.

Once a block has been removed from the mold, the straight-line distancebetween each measurement location and the rear face of the block can bemeasured. The measured straight line distances may be compared with atarget straight line distance. If the measured straight line distancesdo not equal the target straight line distances, one knows that unevendensification has occurred across the front face of the block or thatthe mold cavity was not filled with the appropriate amount of concrete.This could indicate that the pressure plates were not oriented properlyrelative to the mold when they compacted the concrete.

For example, referring to FIG. 6, the straight-line distance X₁ on theblock 54 from the measurement location 56 a to the rear face 46 and thestraight-line distance X₂ on the block 54 from the measurement location56 b to the rear face 46 are measured. Similarly, the straight-linedistances Y₁ and Y₂ for the block 58 in FIG. 7 can be measured. In thedisclosed embodiment, the front faces 44, 44′, 44′ are inclinedrearwardly from the bottom edge to the top edge at a slight angle, forexample, 10 degrees. As a result, the target values of X₁ and X₂ willgenerally be greater than Y₁ and Y₂.

If the block has been properly formed, X₁, X₂, Y₁, and Y₂ will eachequal their respective target distances. On the other hand, if themeasured distances X₁, X₂, Y₁, and Y₂ do not substantially equal thetarget distances, the person conducting the measurement knows that theexpected densification did not take place. Further, if distance X₁ doesnot equal the target distance (or if X₂, Y₁, or Y₂ do not equal theirtarget distances), one knows that uneven densification has occurredacross the front face of the block. This could indicate that thestripper shoe was not level when it compacted the concrete.

Furthermore, with respect to FIG. 2, for any given production cycle, thedistance measurements taken from the block formed in the cavity 10A canbe compared with the distance measurements taken from the block formedin the cavity 10B. If the compression head and stripper shoes have beenproperly configured, the distance measurements for the block from cavity10A and the block from cavity 10B will each equal the target distance.If there is a discrepancy in the measured distances and the targetdistances, that may be an indication that the compression head and/orstripper shoes are not level from one end of the mold to the other andneed to be adjusted, or that the compression head and/or stripper shoesare not level from one side of the mold to the other side and need to beadjusted.

Similarly, with respect to FIG. 3, for any given production cycle, thedistance measurements on the blocks from the cavities 10C, 10D, 10E and10F can be taken and compared against the target distance to determinewhether the compression head and/or stripper shoes are not level fromone end of the mold to the other end and/or not level from one side tothe other side of the mold. With respect to FIG. 3, the blocks in thecavities 10C, 10D, 10E and 10F could be formed with a single measurementlocation, rather than a pair of measurement locations. With a singlemeasurement location on the blocks, one would still be able to determinewhether the compression head and/or stripper shoes is level from one endof the mold to the other end and/or level from one side to the otherside of the mold.

Similarly, the measurements of one set of blocks from one productioncycle can be compared with the corresponding measurements of one set ofblocks from a different production cycle to determine whether the blocksare being formed consistently from one production cycle to the next.

1. A process for producing a plurality of concrete blocks, each blockhaving upper and lower faces, a three-dimensional patterned front face,a rear face and opposed side faces, comprising: providing a mold havingat least one row of block-forming cavities, each block-forming cavityhaving an open top and an open bottom; positioning a pallet underneaththe block-forming cavities to temporarily close the open bottoms of theblock-forming cavities; introducing dry cast concrete into theblock-forming cavities through the open tops of the block-formingcavities; compacting the dry cast concrete in each block-forming cavityto form pre-cured concrete blocks with the rear faces of the blocksresting on the pallet and the front faces of the blocks facing upward,the compacting step including introducing stripper shoes, each of whichhas a face that comprises a three-dimensional pattern, into the cavitiesthrough the open tops and pressing the patterned faces of the strippershoes against the dry cast concrete contained in the mold cavities toimpart patterns to the front faces of the pre-cured concrete blocks, andthe stripper shoes introduced into the block-forming cavities having atotal of at least three separate areas formed on their faces that createa total of at least three measurement locations on the front faces ofthe pre-cured concrete blocks formed in the mold; reopening thetemporarily-closed bottoms of the cavities; discharging the pre-curedconcrete blocks from the cavities through the reopened bottoms of thecavities; and measuring the respective distances between the measurementlocations on the front face and the rear face.
 2. The method of claim 1,wherein the step of measuring the distances between the measurementlocations and the rear face further comprises comparing a measureddistance to a target distance.
 3. The process of claim 1, wherein thestep of providing a mold comprises providing a mold having a first blockforming cavity at one end of the row and a second block forming cavityat an opposite end of the row, and the compacting step includes creatingat least two measurement locations on the front faces of the pre-curedconcrete blocks formed in each of the first and second cavities.
 4. Theprocess of claim 3, wherein the measurement locations on the front faceof the pre-cured concrete block formed in the first cavity are formed onthe front face adjacent the lower face of the block, and the measurementlocations on the front face of the pre-cured concrete block formed inthe second cavity are formed on the front face adjacent the upper faceof the block.
 5. The process of claim 1, wherein the step of providing amold comprises providing a mold having two rows of block-formingcavities, each of the rows having a first block-forming cavity at oneend of the respective row and a second block-forming cavity at anopposite end of the respective row, and the compacting step includescreating at least one measurement location on the front faces of thepre-cured concrete blocks formed in each of the first and secondcavities.
 6. The process of claim 5, wherein the compacting stepincludes creating at least two measurement locations on the front facesof the pre-cured concrete blocks formed in each of the first and secondcavities.
 7. The process of claim 5, wherein for each of the pre-curedblocks formed in the first and second cavities, one of the measurementlocations is formed on the front face adjacent one side face of theblock and one of the measurements locations is formed on the front faceadjacent the other side face of the block.
 8. A method of qualitycontrol in producing a plurality of concrete blocks in a mold having atleast one row of block-forming cavities, each block having upper andlower faces, a three-dimensional patterned front face that is impartedby a three-dimensional pattern on a stripper shoe, a rear face andopposed side faces, comprising: creating a total of at least threemeasurement locations on the front faces of the concrete blocks formedin the mold; and measuring the respective distances between themeasurement locations on the front face and the rear face.
 9. The methodof claim 8, comprising comparing the measured distances with the targetdistances.
 10. The method of claim 8, wherein the mold has a firstblock-forming cavity at one end of the row and a second block-formingcavity at an opposite end of the row, and comprising creating at leasttwo measurement locations on the front faces of the concrete blocksformed in the first and second block-forming cavities.
 11. The method ofclaim 8, wherein the mold has first and second rows of block-formingcavities, each of the rows having a first block-forming cavity at oneend of the respective row and a second block-forming cavity at anopposite end of the respective row, and comprising creating at least onemeasurement location on the front faces of the concrete blocks formed ineach of the first and second block-forming cavities.
 12. The method ofclaim 11, comprising comparing the measurement on a block formed in thefirst cavity of the first row to a target distance and comparing themeasurement on a block formed in the first cavity of the second row to atarget distance.
 13. The method of claim 11, comprising comparing themeasurement on a block formed in the second cavity of the first row to atarget distance and comparing the measurement on a block formed in thesecond cavity of the second row to a target distance.
 14. The method ofclaim 11, comprising comparing the measurements taken on blocks formedin the first and second cavities of the first row to target distancesand comparing the measurements taken on blocks formed in the first andsecond cavities of the second row to target distances.
 15. A method ofverifying the accuracy of a molding process in which a plurality ofconcrete blocks are produced in a mold having at least one row ofblock-forming cavities, and where each block is formed with its frontface facing upward so that a three-dimensional pattern can be impartedto the front face by a three-dimensional pattern on a stripper shoe,comprising: creating at least three measurement locations on the frontfaces of the concrete blocks using the stripper shoes; measuring therespective distances between the measurement locations on the frontfaces and the rear faces; and comparing the measurements to a targetvalue.
 16. The method of claim 15, wherein the step of creatingmeasurement locations on the concrete blocks comprises creatingmeasurement locations on the blocks formed in the end cavities of themold.
 17. The method of claim 15, wherein the step of creatingmeasurement locations on the concrete blocks comprises creatingmeasurement locations that are generally rectangular.
 18. The method ofclaim 17, wherein the rectangular measurement locations areapproximately one-half inch by one-eighth inch.